Vibration damping system

ABSTRACT

The invention relates to a vibration damping system, which comprises an anti-vibration plate in the form of a plate having a first and a second major surface, wherein the first major surface may preferably be covered with a layer of surfactant-free geotextile. The anti-vibration plate comprises one or more layers, preferably a top layer and one or more bottom layers. Furthermore, it is essential that the anti-vibration plate is preferably obtainable by a method comprising the step of subjecting an area of the opposite surfaces of the plate to a compression treatment in one or more steps, which compression treatment is sufficient to reduce the static and/or the dynamic stiffness of the plate compared to the static and/or dynamic stiffness prior to the compression. The invention also relates to the method of applying a vibration damping system and the use of a vibration damping system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vibration damping system, especially for usein the damping of vibrations, e.g., from trains, other traffic anddamping of ground borne vibrations in general.

2. The Prior Art

In the prior art, it is well known to incorporate elastic material undertraffic lines and in particular under tracks for trains, trolley busses,tramcars and similar traffic lines in order to damp the vibrationscaused by this heavy traffic. In the prior art material layers ofelastic material especially made from rubber, PUR-foams and cork,respectively, as well as combinations thereof, have been used fordamping such vibrations.

One of the preferred materials for the damping of vibrations has so farbeen plates or mats of vulcanised rubber which have excellent elasticproperties for use as vibration damping material. Vibration dampingconstructions, wherein the vibration damping elements are constituted byrubber, have in most situations an acceptable vibration dampingefficiency; however, the amount of rubber necessary in suchconstructions in many situations results in a relatively expensiveproduct. Furthermore, there can be a general interest to avoid or reducethe use of rubber materials due to environmental pollution during itsproduction and pollution due to escape of additives, e.g., softeningadditives during use in moist environments, U.S. Patent No. 5,060,856describes such an elastomeric mat for use, e.g., in damping of the soundfrom trains.

It has also been tried to use a mineral fibre board as sound dampingmaterial in railway construction, e.g. as disclosed in DE 35 27 829 andin EP patent publication no. 922 808. This sound damping system hasshown to be very good in certain situations.

In general, it has been found that the use of mineral fibre mats orboards in vibration damping systems for railway foundations is highlydesirable due to adequate performance, easy installation, 100% recyclingability, low pollution effect and a competitive price. However with theknown mineral fibreboards there is a risk, when it is used over a longperiod under high loads, such as the forces from ballast gravels duringpassage of train, that this may have an effect on the mineral fibrematerial over time. This ageing effect is also seen with some of theknown rubber and PUR-materials.

By incorporating the above materials in railway tracks for dampingvibration, it has been observed that there is a risk that the load frompassing trains imposed in the vibration damping system causes an ageingof such system over time. Such ageing is characterized by a change instatic and dynamic stiffness of the anti-vibration plate of thevibration damping system, which is unwanted. For instance, the staticand the dynamic stiffness of the anti-vibration plate may decreasesignificantly during the first 5 to 10 years of use.

Normally it is desired that a vibration damping system under railwaysshould have a durability of about 40 years. A minimum demand fromDeutsche Bahn-Norm (Technische Lieferbedingungen BN 918 071-1, September2000) is that through mechanical excitation the static stiffness of theanti-vibration plate of the vibration damping system may not decrease orincrease more than about 10-20% during a simulated 40 years period inthe laboratory.

According to standard and practical experience the static and dynamicstiffness should preferably be substantially constant over time.

Accordingly, there remains a need for a vibration damping system of theabove-mentioned kind which does not exhibit the above-identifieddrawbacks.

The object of the invention is therefore to provide a vibration dampingsystem comprising an anti-vibration plate with improved stability withrespect to static and particularly dynamic stiffness, and preferablycomprising an anti-vibration plate with a substantially constant staticand dynamic stiffness during its life time defined as 40 years.

Another object of the invention is to provide a vibration damping systemcomprising an anti-vibration plate having an upper surface which issufficiently strong to withstand and distribute the forces from theballast layer. This surface protects the bottom layer or the elasticpart of the mineral fibre board. Furthermore, the surface should bedesigned so that the ballast layer can be replaced. The ballast layerreplacement may be carried out three or four times within the lifetimeof the vibration damping system.

SUMMARY OF THE INVENTION

These and other objects are achieved by the vibration damping system aswhich includes an anti-vibration plate in the form of a plate having afirst and a second major surface, wherein the first major surface maypreferably be covered with a layer of surfactant-free geotextile. Theanti-vibration plate includes one or more layers, preferably a top layerand one or more bottom layers. The top layer and the one or more bottomlayers both include mineral fibres and a binder, preferably a curedbinder.

The vibration damping system according to the invention has shown topossess a very high vibration damping effect, whereby undesiredvibrations from railway traffic and likewise can be reduced to anacceptable level or even be substantially eliminated. It has been foundthat the vibration damping effect of the vibration damping system isonly slightly or not at all influenced by the temperature of thesurrounding environment, which means that the system works effectivelyunder a wide range of temperatures.

Furthermore, the installed vibration damping system according to theinvention is competitive with respect to vibration damping systemscomposed of e.g. rubber alone. Another desired property of the vibrationdamping system is its durability which is highly increased due to theconstruction, because gravel, stone, soil, asphalt and other coveringmaterials do not result in significant deterioration of the mineralfibre material.

In a preferred embodiment of the vibration damping system according tothe invention the anti-vibration plate comprises at least a top layerand one or more bottom layers. The top layer is in the form of apressure distributing layer and the one or more bottom layers in theform of a vibration damping layer. The top layer and the one or morebottom layers may have different densities, different thicknesses andcomprise different amount of binder.

The top layer preferably has a density of 250-400 kg/m³ more preferably300-350 kg/m³ and has a thickness of 5-20 mm, more preferably 10-15 mm,and comprises a binder of preferably at least 4-6% by weight.

The one or more bottom layers preferably have a density of 100-250kg/m³, more preferably 180-200 kg/m³, and have a thickness of 5-150 mm,preferably 35 mm, and comprise a binder of preferably 3-5% by weight.

Each of the layers of mineral fibres should preferably comprise at least20%, preferably at least 50% and more preferably at least 80% by weightof one or more types of mineral fibres, e.g. rock, slag, glass andsimilar vitreous materials.

Furthermore it is essential that the anti-vibration plate is preferablyobtainable by a method comprising the step of subjecting an area of theopposite surfaces of the plate to a compression treatment in one or moresteps, which compression treatment is sufficient to reduce the staticand/or the dynamic stiffness of the plate by at least 10%, preferably atleast 15%, more preferably at least 20%, compared to the static and/ordynamic stiffness prior to the compression. An anti-vibration plateobtainable by this method thus has a constant perfomance, that is aconstant static and dynamic stiffness over time.

In a preferred embodiment the anti-vibration plate is obtainable by amethod comprising the step of subjecting an area of the oppositesurfaces of the plate to a compression treatment, wherein thecompression treatment comprises the step of subjecting an area of theopposite surfaces of the plate at the compression pressure in theinterval from 50 to 250 kN/m², preferably from 80 to 200 and morepreferably from 100 to 150 kN/m², whereby the static and/or dynamicstiffness of the plate measured according to the method defined inDeutsche Bahn-Norm BN 918 071-1 (September 2000) is reduced compared tothe static stiffness prior to the compression treatment.

In general, it is insignificant which method has been used forsubjecting the opposite surfaces of the plate to the compressiontreatment, however, due to the object to provide a simple and economicalmethod, and thereby an economically acceptable product, theanti-vibration plate can be obtained by a method comprising the step ofsubjecting the plate to a compression treatment by rolling through oneor more pairs of rollers, thereby providing a nip between the one ormore rollers making contact with the first major surface and the one ormore rollers making contact with the second major surface.

When using this method, the one or more pairs of rollers could have sameor different diameters. In a preferred embodiment the one or morerollers in contact with the first major surface have a diametersubstantially higher than the thickness of the antivibration plate, e.g.in the ratio 10:1, preferably 8:1, more preferably 6:1, and mostpreferably 2:1. The one or more rollers in contact with the second majorsurface have a diameter substantilly lower than the thickness of theantivibration plate, e.g. in the ratio 1:10, preferably 1:8, morepreferably, 1:6 and most preferably 1:2. The one or more rollers incontact with the first major surface or second major surface having adiameter substantially higher or lower than the thickness of theantivibration plate result in different pressures being exerted over thesurface of the antivibration plate.

In another preferred embodiment of the invention, the compressiontreatment of the anti-vibration plates may be carried out by joining twoanti-vibration plates so that the higher density layers of the platesface each other. The composite anti-vibration plate can be subjected toa compression treatment by rolling it through one or more pair ofrollers, thus providing a nip between the one or more rollers makingcontact with the second major surface of the one anti-vibration plate,i.e. its lower density layer, and the one or more rollers making contactwith the second major surface of the other anti-vibration plate, i.e.its lower density layer. When using this method, the one or more pairsof rollers could have the same or different diameters, said diametersbeing preferably smaller than the thickness of either anti-vibrationplate.

In a further preferred embodiment of the invention the anti-vibrationplates comprising two layers of different densities may be stacked oneon top of another to conform a transport unit, wherein the higherdensity layer of each anti-vibration plate faces the lower density layerof the adjacent anti-vibration plate of the stack. The transport unit asa single entity is thereafter subjected to a compression step over thesurface of its uppermost surface.

The anti-vibration plate or at least the exposed surfaces of the platemay be hydrophobic. The surface tension of the fibre material of theplate should preferably not be higher than the surface tension of thenatural non-bonded and treated fibres. In some embodiments the plateshould preferably be sufficiently hydrophobic to avoid any substantialentrance of water, when water drops at 20° C. are sprayed onto theplate. Particularly, it is preferred that the anti-vibration plate has asurface tension below 73 dynes/cm, e.g. having a surface tension below40 or even below 30 dynes/cm.

Methods of making the mineral fibres hydrophobic are well known in theart.

The vibration damping system according to the invention may alsocomprise two or more anti-vibration plates placed upon each other wherethe edge or edges of the plates are placed in distance from each otherin order to cover joints. If the plates have different densities, theplate with the higher density should preferably be placed upon the platewith the lower density.

During the life time of an anti-vibration plate, the ballast layer maybe exchanged several times. In order to provide a strong and resistantsurface of the anti-vibration plate to increase its ability to withstandexchanges of ballast layer, the anti-vibration plate is covered on thefirst of its major side surfaces with a layer of surfactant-freegeotextile.

The geotextile may in principle be any type of geotextile provided thatit is surfactant-free. By the term “geotextile” is meant any flexibleplane structure of fibres.

By the term “surfactant-free” is meant that the fibres of the geotextilehave not been treated with a surfactant, which in this application meansa wetting agent or a tenside (surface tension decreasing agent).

The surfactant-free geotextile should preferably have a thickness of atleast 0.1 mm, more preferably between 0.4 and 3 mm measured according toEN 964-1 under a load of 2 kN/m². A thickness between 0.5 and 1 mm willin most applications be optimal.

The surfactant-free geotextile may preferably be selected from the groupconsisting of staple fibre, continuous non-woven filament,thread-structure mats and strip mats. In a preferred embodiment thesurfactant-free geotextile is a non-woven textile. These types of matsand their preparation are generally known to a skilled person. It hasbeen found that a non-woven surfactant-free geotextile in generalprovides the anti-vibration plate with an optimal surface protection.The surfactant-free geotextile may e.g. be substantially watertight oralternatively it may be permeable to water.

The surfactant-free geotextile could in principle be of any kind ofmaterial. However, in order to obtain a stable and sufficiently stronggeotextile, it is preferred that the surfactant-free geotextile is madefrom fibres, threads or filaments of a material selected from the groupconsisting of polyester, polyamide, polypropylene, polyether,polyethylene, polyetheramide, polyacrylnitrile, glass or a combinationthereof. The surfactant free geotextile is preferably made from fibresor filaments of polyamide coated polyester or polypropylene.

The surfactant-free geotextile may preferably be fixed to theanti-vibration plate e.g. by heat fusing or gluing.

In order to protect the anti-vibration plate to an optimal degree, thesurfactant-free geotextile should preferably have a tensile strength ofat least 8 kN/m, preferably at least 20 kN/m measured according to ENISO 10319. Preferably the surfactant-free geotextile should have atensile strength in all directions of its plane which is above 8 kN/m.

Useful structures of geotextile are e.g. the geotextile marketed underthe trade name “Typar® SF” by DuPont® Nonwovens.

In the vibration damping system according to the invention theanti-vibration plate may be more or less covered by the surfactant-freegeotextile along one or more of the two major surfaces. Theanti-vibration plate may e.g. be totally coated by the surfactant-freegeotextile or it may be coated on its first major surface. In mostembodiments it is not necessary to cover more than the first majorsurface of the anti-vibration plate and since the surfactant-freegeotextile is relatively expensive, it is normally avoided to cover morethan the first major surface of the anti-vibration plate. Depending onthe ground surface condition it may be necessary to cover the secondmajor surface also.

The vibration damping system may preferably further comprise a layer ofa drain-core material comprising a three-dimensional matting of loopedfilaments.

The looped filaments should preferably have a sufficiently high strengthto avoid a complete and permanent collapse under the load of the gravel,stones or similar covering materials, which may be covering thevibration damping system. It is preferred that the looped filaments aremade of polymeric monofilaments welded together where they cross,whereby an open structure with an open volume is provided. The loopedfilaments of the drain-core layer are preferably made from a materialselected from the group consisting of polyamide, polyester, high-densitypolyethylene, polystyrene and combinations thereof. A particularlypreferred material for the production of the looped filaments of thedrain-core layer is polyamide.

The open volume should preferably constitute 80% or more of the totalvolume of the drain-core layer. The drain-core layer should preferablybe placed between the first major surface of the anti-vibration plateand the covering layer of surfactant-free geotextile.

In a preferred embodiment of the vibration damping system according tothe invention the vibration damping system further comprises a secondlayer of geotextile placed between the first major surface of theanti-vibration plate and the drain-core layer. Thus, this preferredembodiment includes a layered product comprising an mineral fibre boardcovered on its first major surface by a draining mat of a drain-corelayer sandwiched between two layers of surfactant-free geotextile.

The thickness of the drain-core layer may preferably be up to about 15mm. Drain-core layers thicker than that tend to be too soft for therequirement of static and dynamic stiffness of the system. Since theprice of the drain-core layer is highly dependent on the height of thisdrain-core layer, it is preferred to use a height as low as possible ofthis layer, where the effect is optimal or at least satisfactory. It ispreferred that the total thickness of the drain-core layer including thelooped polyamide filaments, the surfactant-free geotextile and thesecond surfactant-free geotextile is at least 3 mm, preferably at least5 mm. In general it is preferred that the surfactant-free geotextile isas thin as possible while still being able to provide a distribution ofthe forces against the underlying mineral fiber board. The geotextilesof the draining mat may preferably be glued or heat melted to thedrain-core layer.

The second surfactant-free geotextile may be selected from the samegroup of materials and be of the same type as the surfactant-freegeotextile as described above. The strength of the secondsurfactant-free geotextile is not so important, and, thus, the secondsurfactant-free geotextile may be of the same thickness as thesurfactant-free geotextile or it may be thinner.

In a particularly preferred embodiment the draining mat is formed fromtwo layers of surfactant-free geotextile of non-woven polyamide coatedpolyester fibres and a looped polyamide filament drain-core layersandwiched between the two surfactant-free geotextile.

Useful draining mats of the above type are e.g. described in DEpublication Nos. DE 2150590 and DE 4431976. A particularly preferredtype of draining mats is marketed by Colbond Geosynthetics, TheNetherlands, under the trade name Enkadrain®.

One or more of the surfaces which are not covered with geotextile maypreferably be covered with a surface coating in the form of a fibrousnetting formed of a thermoplastic polymer material. Particularly, it ispreferred that one or more side surfaces of the anti-vibration plate arecovered with such a surface coating in the form of a fibrous netting.Such covering material is further described in EP 629153.

The invention also relates to a method of preparing an anti-vibrationplate according to the invention comprising the steps of preparing aplate comprising one or more layers, preferably a top layer and one ormore bottom layers as defined above, and subjecting an area of theopposite surfaces of the plate to a compression treatment in one or moresteps, which compression treatment is sufficient to reduce the staticand/or the dynamic stiffness of the plate by at least 10%, preferably atleast 15%, more preferably at least 20% compared to the static and/ordynamic stiffness prior to the compression treatment.

As mentioned above it is in general insignificant which method has beenused for subjecting the opposite surfaces of the plate to thecompression treatment, but it is preferred that the method comprises thestep of subjecting the plate to a compression treatment by rollingthrough one or more pairs of rollers, thereby providing a nip betweenthe one or more rollers making contact with the first major surface andthe one or more rollers making contact with the second major surface.When using this method, the one or more pairs of rollers could have sameor different diameters.

In a preferred embodiment the one or more rollers in contact with thefirst major surface have a diameter substantially higher than thethickness of the antivibration plate, e.g. in the ratio 10:1, preferably8:1, more preferably 6:1, and most preferably 2:1. The one or morerollers in contact with the second major surface have a diametersubstantilly lower than the thickness of the antivibration plate, e.g.in the ratio 1:10, preferably 1:8, more preferably, 1:6 and mostpreferably 1:2. The one or more rollers in contact with the first majorsurface or second major surface having a diameter substantially higheror lower than the thickness of the antivibration plate result indifferent pressures being exerted over the surface of the antivibrationplate.

The invention also relates to a method of applying a vibration dampingsystem to a ground subjected to vibrations.

The method comprises the steps of:

-   -   i providing an anti-vibration plate, preferably using the method        as described above;    -   ii applying a layer of surfactant free geotextile onto the first        major surface;    -   iii optionally covering one or more surfaces of the        anti-vibration plate as described above;    -   iv applying the anti-vibration plate onto the ground with its        first major surface upwardly prior to or after the application        of the surfactant free geotextile onto the first major surface;    -   v covering the first major surface of the anti-vibration plate        with concrete, stone, gravel, soil and/or asphalt.

Prior to the application of the vibration damping system the ground maypreferably be prepared e.g. by levelling the ground in the depression inthe ground, where the vibration damping system is to be applied.Furthermore, the ground may preferably be further stabilised e.g. bycovering the ground with a material selected from the group consistingof water pervious foil, granulates of rubber, gravel or mixturesthereof.

If the major surface of the anti-vibration plate is covered with acovering layer in the form of a surfactant-free geotextile and/ordrain-core layer or a draining mat, it is preferred that thesurfactant-free geotextile and the anti-vibration plate are glued, sewedor heat fused together. This may be done on ground or in factory.

Alternatively, the anti-vibration plate may first be applied to theground and thereafter a covering layer in the form of a surfactant-freegeotextile and/or drain-core layer or a draining mat is applied onto thefirst major side of the anti-vibration plate.

If the vibration damping system further comprises a drain-core layerand/or a second layer of surfactant-free geotextile, these layers may beapplied one by one onto the anti-vibration plate prior to theapplication of the surfactant-free geotextile, or these layers may beapplied together with the surfactant-free geotextile in the form of adraining mat as defined above.

The draining mat may preferably be applied from a roll of draining matmaterial directly onto the anti-vibration plate or plates. It ispreferred that the draining mat material from one roll covers two ormore anti-vibrations plates. The width of the roll of draining matmaterial should preferably be at least substantially equal to the widthof the anti-vibration plates.

When the vibration damping system has been safely applied, the firstsurface of the anti-vibration plate or optionally the covered firstsurface of the anti-vibration plate board may further be covered withconcrete, stone, gravel, soil and/or asphalt or similar materials.Finally, a railway track may be applied onto the vibration dampingsystem.

The vibration damping system according to the invention is preferablyused for damping the vibrations caused by trains, trolley busses,tramcars and/or other traffic on a railway or roadway, wherein the usecomprises incorporation of the vibration damping system in the groundunder the railway and/or road.

EXAMPLE

An anti-vibration plate according to the invention having a first and asecond major surface was provided as described in the following. Theanti-vibration plate was made from rock wool. The anti-vibration platecomprised two layers, a top layer and a bottom layer. The top layer hada density of 350 kg/M³, a thickness of 15 mm, and comprised a binder of6% by weight. The bottom layer had a density of 200 kg/m³, a thicknessof 35 mm, and comprised a binder of 4% by weight. The dimension of theanti-vibration plate was about 35 mm×600 mm×100 mm. The anti-vibrationplate was obtained by a method comprising the step of subjecting an areaof the plate to a compression treatment. The compression treatment wasmade through rollers having different diameters. The compressiontreatment reduced the static and dynamic stiffness of the plate by about10-20% compared to the static and dynamic stiffness prior to thecompression. The static stiffness before the compression treatment was0,025 N/mm³ and after the compression treatment it was 0,020 N/mm³,measured according to the method defined in BN 918 071-1. The dynamicstiffness before the compression treatment was 0,027 N/mm³ and after thecompression treatment it was 0,024 N/mm³, measured according to themethod defined in BN 918 071-1.

1. A method of making an anti-vibration plate for a vibration dampingsystem, comprising the steps of: a) providing a plate having a firstmajor surface and an opposite second major surface, said platecomprising one or more layers comprising mineral fibres and a curedbinder, and b) compressing an area of said opposite first and secondmajor surfaces of said plate provided in step (a) to reduce the staticand/or dynamic stiffness of the plate by at least 10% compared to astatic and/or the dynamic stiffness of said plate prior to step (b),said plate provided in step a) comprising two of said layers comprisingmineral fibers and cured binder, one of said layers defining a top layerand the other defining a bottom layer, said top layer defining saidfirst major surface and said bottom layer defining said second majorsurface, said top layer and said bottom layers having differentdensities.
 2. A method according to claim 1, wherein said compressingstep involves applying a pressure of between 50 and 250 KN/m².
 3. Amethod according to claim 1, wherein said compressing step comprisesapply a pressure of between 80 and 200 KN/m².
 4. A method according toclaim 1, wherein said compressing step comprises applying a pressure ofbetween 100 and 150 KN/m².
 5. A method according to claim 1, whereinsaid layers having different amounts of said binder.
 6. A methodaccording to claim 1, wherein said plate provided in step a) has morethan two of said layers comprising mineral fibers and cured binder, saidlayers having different thicknesses.
 7. A method according to claim 1,wherein said plate provided in step a) has more than two of said layerscomprising mineral fibers and cured binder, said layers having differentamounts of said binder.
 8. A method according to claim 1, wherein saidmineral fibers are rock wool fibers.
 9. A method according to claim 1,wherein after step b) a layer of surfactant free geotextile is appliedon said first major surface.
 10. A method according to claim 1, whereinsaid layers comprise at least 20% a by weight of said mineral fibres.11. method according to claim 1, wherein said layers comprise at least50% a by weight of said mineral fibres.
 12. A method according to claim1, wherein said layers comprise at least 80% a by weight of said mineralfibres.
 13. A method of installing a vibration damping system on aground surface comprising the steps of providing a vibration dampingsystem comprising an anti-vibration plate having a first major surfaceand an opposite second major surface, said anti-vibration platecomprising one or more layers comprising mineral fibres and a curedbinder, wherein said opposite major surfaces of said anti-vibrationplate having been subjected to a compression treatment after curing toreduce the static and/or dynamic stiffness of said anti-vibration plateby at least 10% , compared to the static and/or the dynamic stiffnessprior to said compression treatment, said anti-vibration platecomprising a top layer in the form of a force distributing layer and oneor more bottom layers in the form of vibration damping layers, said toplayer and at least one of said bottom layers having different densities,different thicknesses and comprising different amounts of binder,placing said vibration damping system on the ground surface, andcovering the first major side of the anti-vibration plate with at leastone of a layer of surfactant-free geotextile, a drain-core layer and adraining mat.